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SubjectRe: [PATCH] iio: adc: at91: disable adc channel interrupt in timeout case
On Wed, 30 Jan 2019 14:42:02 +0100
<g.ottinger@abatec.at> wrote:

> From: Georg Ottinger <g.ottinger@abatec.at>
>
> Having a brief look at at91_adc_read_raw() it is obvious that in the case
> of a timeout the setting of AT91_ADC_CHDR and AT91_ADC_IDR registers is
> omitted. If 2 different channels are queried we can end up with a
> situation where two interrupts are enabled, but only one interrupt is
> cleared in the interrupt handler. Resulting in a interrupt loop and a
> system hang.
>
> Signed-off-by: Georg Ottinger <g.ottinger@abatec.at>

Whilst I agree this looks like a correct change, I would like Maxime
to take a look as he is obviously much more familiar with the driver
than I am.

I suspect you can only actually get there in the event of a hardware
failure as that isn't actually a timeout you should ever see.
Could be wrong though!

Thanks,

Jonathan

> ---
> drivers/iio/adc/at91_adc.c | 28 +++++++++++++++++-----------
> 1 file changed, 17 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
> index 75d2f7358..596841a3c 100644
> --- a/drivers/iio/adc/at91_adc.c
> +++ b/drivers/iio/adc/at91_adc.c
> @@ -704,23 +704,29 @@ static int at91_adc_read_raw(struct iio_dev *idev,
> ret = wait_event_interruptible_timeout(st->wq_data_avail,
> st->done,
> msecs_to_jiffies(1000));
> - if (ret == 0)
> - ret = -ETIMEDOUT;
> - if (ret < 0) {
> - mutex_unlock(&st->lock);
> - return ret;
> - }
> -
> - *val = st->last_value;
>
> + /* Disable interrupts, regardless if adc conversion was
> + * successful or not
> + */
> at91_adc_writel(st, AT91_ADC_CHDR,
> AT91_ADC_CH(chan->channel));
> at91_adc_writel(st, AT91_ADC_IDR, BIT(chan->channel));
>
> - st->last_value = 0;
> - st->done = false;
> + if (ret > 0) {
> + /* a valid conversion took place */
> + *val = st->last_value;
> + st->last_value = 0;
> + st->done = false;
> + ret = IIO_VAL_INT;
> + } else if (ret == 0) {
> + /* conversion timeout */
> + dev_err(&idev->dev, "ADC Channel %d timeout.\n",
> + chan->channel);
> + ret = -ETIMEDOUT;
> + }
> +
> mutex_unlock(&st->lock);
> - return IIO_VAL_INT;
> + return ret;
>
> case IIO_CHAN_INFO_SCALE:
> *val = st->vref_mv;

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